PROJECT SUMMARY: No changes from initial submission There is an urgent need to develop novel therapies for patients with medulloblastoma (MB), the most common malignant central nervous system (CNS) tumor in children. Current treatments include surgery, radiotherapy, and chemotherapy and result in 5-year survival rates of 40-90% depending on subtype. However, children suffer important morbidity secondary to treatment, including neurological, intellectual and physical disabilities. The overall purpose of the present project is to investigate the role of the ADGRB3 receptor in susceptibility of cerebellar transformation, and explore new therapies for MB based on the related mechanisms. ADGRB3 is an orphan seven transmembrane G protein-coupled receptor (GPCR) specifically expressed in the brain, and belonging to the adhesion-type sub-family. Our new preliminary data show that ADGRB3 expression is significantly reduced in patients with MBs of the WNT group, and the promoter is epigenetically silenced, suggesting that ADGRB3 loss may facilitate WNT-MB formation. We present evidence for the involvement of methylated CpG binding protein MBD2 and histone methyltransferase EZH2 in switch to a silent chromatin. Moreover, we show that reactivation of ADGRB3 can reduce cell proliferation and tumor growth, supporting a tumor suppressive role. To test this in the physiological setting, we generated ADGRB3 knockout (KO) mice, which we plan to cross with mice expressing mutant b-catenin in neural progenitors of the rhombic lip and dorsal brainstem, which are the cells of origin of WNT-MB. Based on these results, we hypothesize that ADGRB3 is a tumor suppressor in the cerebellum and that restoration of its expression with epigenetic therapy may represent a novel therapeutic intervention for children with WNT-MB. To test our hypothesis, we propose the following aims: (i) identify and target the epigenetic mechanism(s) underlying ADGRB3 gene silencing in WNT-MB, (ii) determine whether and how restoration of ADGRB3 expression can inhibit MB cell growth, oncogenic signaling and tumorigenic properties, and (iii) determine whether loss of ADGRB3 gene expression in the background of oncogenic Ctnnb1 activation predisposes mice to cerebellar transformation and MB tumor development. These studies are important as they increase our knowledge about developmental neurobiology in the CNS, and may lead to the development of novel therapeutic approaches for patients with medulloblastoma.